Apparatus for driving board drains underground

ABSTRACT

For the consolidation of soft-clay soils, board drains are placed in the soils by inserting each board drain into a hollow mandrel, fixing the end of the board drain to a cap attached on the lower end of the mandrel, driving the mandrel with the board drain inside into the soil to a desired depth, then pulling up the mandrel proper, leaving the board drain-holding cap behind in the soil. Soil water flows out of the voids through the board drains.

United States Patent 11 1 1111 3,881,319 Katagiri et al. 1 May 6, 1975 [54] APPARATUS FOR DRIVING BOARD 1,085,430 1/1914 Kahn 61/5366 BRAINS UNDERGROUND 1,275,470 8/1918 Pruyn 61/53] 2,577,252 l2/195l Kjellman....... 6l/ll [75] In t rs: K ta atag Yokohama; 3,797,251 3 1974 Smimizv.... 61/11 Masayuki Saito, KodairagJiro Saito, 3,797,252 3/1974 Ohtsuka...... .1 61/535 Tokyo; Kiyoshige Nishibayashi, Niiza; Tatsuyuki Matsuo, Tokorozawav an of Japan Primary ExaminerPaul R. Gilliam [73] Assignees: Shinetsn Chemical Company, Assistant Examiner-Mex GYOSZ Tokyo; 0hbayashi GumL Ltd" Attorney, Agent, or Fzrm-B1erman & Blerman Osaka, both of Japan [22] Filed: Oct. 3, 1973 21 Appl. No.: 403,069 57 ABSTRACT [30] Foreign Application Priority Data For the consolidation of soft-clay soils, board drains 061. s, 1972 Japan 47-100121 are Placed in the Soils y inserting each hoard drain into a hollow mandrel, fixing the end of the board 52 us. (:1. 61/11; 61/63 drain to a p attached on the lower end of the 51 1111.021 E02b 11/00 drel. driving the mandrel with the beard drain inside [58] Field 61 seal'dl 61/11, 13, 53.64, 53.66, into the to a desired depth, Pulling p the 61153.7, 63; 52/155, 742, 158, 165 mandrel proper, leaving the board drain-holding cap behind in the soil. Soil water flows out of the voids 5 References Cited through the board drains.

UNlTED STATES PATENTS 790,910 5/1905 McClintock 61/537 8 Claims, 10 Drawing Figures PATENIED HAY 61875 SHEET 2 [1F 3 Fig.3

minnow 61915 1381319 SHEEI 38? 3 Fig.4 Fig.5

Fig.6 Fig-7 APPARATUS FOR DRIVING BOARD DRAINS UNDERGROUND FIELD OF THE INVENTION This invention relates to improvements in the method of driving underground board drains, such as card boards and synthetic boards, for the consolidation of soft-clay soils.

DESCRIPTION OF THE PRIOR ART There is known the socalled Kjellmans cardboard drain method for consolidating fine-grain soils, in which card-board wicks are driven underground so that soil water flows out of the voids through the drain wicks as pressure is applied to the ground. According to the card-board drain method, card boards are driven into the ground usually by the following steps: (I) a card board drain is guided into a hollow mandrel vertically sustained on the ground to its full length from a reel of the card board stock by way of a feed means comprising a pair of back rolls provided at top of the mandrel, (2) the mandrel is driven underground to a desired depth with the card board held by the back rollers (3) the mandrel proper is thoroughly pulled up above the ground, leaving the card board behind in the soil, while the back rollers are rotated, and thereafter (4) the card board is cut off by an auto-cutter about 30 cm above the ground surface.

In practicing the above card-board drain driving method, it is required to specifically design the mandrel construction such that the lower end of mandrel should be closed to prevent any sand and water from entering thereinto while the mandrel is driven and that the card board should be passed in the mandrel without any difficulty at a rate corresponding to that of the mandrel during the withdrawal of the mandrel out of the ground.

Further, according to the conventional method, the lowest end of the mandrel is liable to break when, for instance, it hits on a hard object like rock during the driving operation, and the card board feeding mechanism tends to suffer failure or breakdown since it is rather complicated. Furthermore, when water and earth pressure are great in the soil, muddy water tends to force into the hollow mandrel, to cause to bond the card board to the inner surface of the mandrel, resulting to make it hard to leave the card board in the soil when the mandrel is pulled up.

OBJECTS OF THE INVENTION The primary object of the present invention is to provide a method of driving a board drain undergound, whereby the board drain is enclosed in a hollow mandrel, drive therewith together and, securely, remains unmoved as is when the mandrel is then pulled out of the ground.

Another object of the present invention is to effectively prevent any muddy water from entering into the hollow mandrel during the driving operation.

Still another object of the present invention is to proved a method wherein the provision of a pair of back rollers of the above-described conventional apparatus can be dispensed with.

SUMMARY OF THE INVENTION The above and other objects are accomplished in accordance with the method of this invention comprising the steps of inserting a board drain into a hollow mandrel, driving the mandrel underground to a desired depth, and then pulling out the mandrel, leaving the board drain behind in the soil. For the purpose, the mandrel is provided, prior to drive, on its lowest end with a cap to which the bottom end of the board drain is fixed and which is designed to remain in the soil after the mandrel has been pulled out of the ground. The most preferred type of the cap is a sort of trough of a bilge-like sectional shape, having centrally on its upper surface an anchor means for fixing the board drain, and when the mandrel is pulled up the longitudinal edges of the cap cut into the soil, to make the cap left as is in the soil with the board drain secured thereto.

Now, the present invention will be described in detail by way of some preferred embodiments thereof with reference to the accompanying drawings. It should, however, be understood that these embodiments are merely intended to be illustrative and not restrictive to the invention.

In the drawings:

FIG. 1 is a schematic sectional view of the end portion of a hollow mandrel including a cap made of plastic material.

FIG. 2 is a perspective view showing a typical cap used in the method of the present invention;

FIG. 3 consists of schematic drawings showing the driving conditions of the hollow mandrel for the purpose of illustrating the driving steps according to the method of the present invention;

FIGS. 4 to 10 show different embodiments of the cap, where each of FIGS. 4 to 7 is a front view with different external surface patterns and each of FIGS. 8 to 10 is a side view with different anchoring or fixing means.

Referring first to FIG. I, there is shown the drilling end portion of a hollow mandrel used for driving a board drain underground by the method of the present invention. In the figure, reference numeral 1 designates a hollow mandrel, 2 a board drain, 3 a cap, and 4 a packing adapted to ensure the prevention of ingress of mud or water into the mandrel from its open end during the driving operation. This packing is not always required in the present invention and is used at need. The board drain used here is one that is capable of effectuating perfect drainage in the consolidation of the soil and can also maintain its high draining performance until completion of the required consolidation. The board drain is along strip, for example, 3 mm thick and mm wide and made from a material which remains noncorrosive when left in the soil for a long time and which has a sufficient water permeability and high wet strength, for example, a kind of thick craft paper, reinforced with resin to improve its water resistance, or a porous sheet made from sintered polyvinyl chloride powder, or a chemical board made from a polymer of polypropylene type.

FIG. 2 shows a typical example of the cap used in the method of the invention. It is a trough-shaped structure 5 having a bilge-like sectional shape, with an anchoring means 6, prvided at the center of the upper surface of the cap, for fixing therein the lowest end of the board drain.

Now, the method of the present invention is de scribed according to its steps with reference to FIG. 3.

First, a board drain 2 is introduced into a hollow mandrel 1 such that the fore end of the board drain is slightly projected out from the extreme end of the mandrel, and fixed to the cap 3. The cap 3 is then inserted into the end opening of the mandrel 1 (FIG. 3(A)), ready for driving underground in a known manner. After the mandrel has been driven to a desired depth (FIG 3(3)), it is pulled up, leaving the board drainholding cap behind in the soil (FIG. 3(C)), til its lower end comes up above the ground surface, and then the board drain is cut off about half-way between the mandrels lowerest end and the ground surface (FIG. 3( D)), to complete one round of the drive work. In this case, although not shown, there may be provided means for ejecting compressed air from the end of the mandrel when it is pulled up, so that the cap may be easily detached from the end of the mandrel.

Thus, according to the method of the present invention, the cap attached to the lowest end of the board drain can be thrust into earth when the mandrel is drawn up and the board drain remains as is in the soil. Further, since the board drain is given a downward pull when the mandrel is raised up, the mechanism for feeding the board drain into the mandrel synchroneously with the upward pull of the mandrel as necessitated in the conventional method is no more required. Furthermore, according to the invention, it is possible to effectively prevent muddy water from entering into the mandrel when it is driven underground. It is another characteristic of the invention that the end portion of the mandrel is protected from possible damage by any hard rock by means of the cap during the driving operation.

The underside configuration of cap 3 is not limitted to the one having a central sharp ridge 8 as shown in FIG. 2, but it may be of a general curvature. However, the one having a sharp ridge substantially along the center line of the underside as shown in FIG. 2 is preferred because such configuration allows easier and smoother driving of the mandrel into earth. The exter nal surface of the cap shown in FIG. 2 is smooth but it is prefereed to provide thereon raised streaks or stripes of various patterns, longitudinally or transversely, as shown in FIGS. 4 to 7, to thereby increase the external surface area of the cap and, consequently, enhance cohesion between the cap and the soil, thus making it more propitious for the cap to be left in the soil behind the mandrel withdrawn.

On the other hand, the cap 3 is configured such as to aptly enclose the lower end portion of the mandrel l, as shown in FIG. I.

Along about the longitudinal center line on the upper surface of cap 3 is provided an anchoring means 6, the size of which should be such that allows easy insertion into the rectangular end opening 7 of the mandrel l. The anchoring means is shown in FIG. 2, comprising a pair of tongues 6 and 6 of the same thickness, arranged in parallel, face to face and slightly spaced apart from each other so that the end of the board drain 3 can be fitted and secured therebetween. FIGS. 8 to 10 show different embodiments of the anchoring means. The embodiment of FIG. 8 consists of a realtively thick tongue and a thiner one, arranged in parallel, face to face. In this case, since the thiner tongue is easy to be bended, the insertion of the board drain between the two tongues is more facilitated. The embodiment shown in FIG. 9 comprises tow tongues, one of which is vertically longer than the other. This combination of tongues also permits easy insertion of the board drain. In applying the insertion of the board drain to the twotongue cap of FIGS. 2, 8 or 9, it is preferred, for example, to provide several protuberances on the inside surface of each tongue and, at the same time, make small apertures at the corresponding points on the board drain to be inserted so that the protuberances are en gaged in corresponding apertures (see FIG. 1), or to fasten both tongues by a fastening machine after the board drain has been interposed between the tongues 6, or to employ these two manners in combination. The embodiment shown in FIG. 10 proposes only one piece of tongue, to which the board drain is simply attached so as to overlap each other and then fastened by a fastening machine.

The caps used in the present invention can be made of various types of synthetic resin material and molded, for example, by the injection molding. The resin material is preferably selected from the viewpoint of me chanical strength and workability, from the group of polyethylene, polypropylene and polyvinyl chloride. The product is advantaged by that, due to the elastic material, its configuration can be subject to change along that of the end of the mandrel to which it is attached, as the driving operation is performed, consequently any resistance against penetration of the mandrel into the soil is greatly lessened to allow a smooth driving operation, and further, the configuration thus changed can be restored to its original shape when the mandrel is pulled up, resulting to make the side walls of the cap easily cut into the earth.

What is claimed is:

1. Apparatus for insertion of board drains into soft clay soils comprising a board drain, a hollow mandrel and a capping means, said hollow mandrel having at least one open end, said capping means having means for securing said board drain thereonto, said capping means surrounding the open end of said mandrel to protect it from entry of foreign matter when the mandrel, capping means and board drain are driven into the soil, and said capping means being provided with two diverging edged wings on opposing sides, said wings ex tending outwardly from the lower end of said hollow mandrel so as to anchor said capping means and said board drain in the soil by cutting the soil when said hollow mandrel is pulled up.

2. The apparatus according to claim I wherein said capping means is provided with a sharp ridge on the lower surface thereof at the point of juncture of said wings.

3. The apparatus according to claim 1 wherein said capping means is provided with a plurality of raised ribs on the said wings.

4. The apparatus according to claim 1 wherein the means for securing the board drain to said capping means comprises a pair of tongues spaced from each other, said tongues being mounted in said capping means, said board drain being mounted between said tongues, and means for securing said board drain to said tongues.

5. The apparatus according to claim 4 wherein said tongues are provided with a plurality of protuberances and said board drain is provided with a plurality of apertures, said protuberances engaging said apertures when said board drain is in place between said tongues.

6. The apparatus according to claim 1 wherein said means for securing said board drain to said capping means comprises a tongue mounted on said capping means, said board drain being mounted adjacent one 6 face of said tongue, and fastening means for securing 8. The apparatus according to claim 1 wherein said said board drain to said tongue. board drain is made of sintered porous polyvinyl chlo- 7. The apparatus according to claim 1 wherein said ride.

board drain is made of water resistant craft paper. 

1. Apparatus for insertion of board drains into soft clay soils comprising a board drain, a hollow mandrel and a capping means, said hollow mandrel having at least one open end, said capping means having means for securing said board drain thereonto, said capping means surrounding the open end of said mandrel to protect it from entry of foreign matter when the mandrel, capping means and board drain are driven into the soil, and said capping means being provided with two diverging edged wings on opposing sides, said wings extending outwardly from the lower end of said hollow mandrel so as to anchor said capping means and said board drain in the soil by cutting the soil when said hollow mandrel is pulled up.
 2. The apparatus according to claim 1 wherein said capping means is provided with a sharp ridge on the lower surface thereof at the point of juncture of said wings.
 3. The apparatus according to claim 1 wherein said capping means is provided with a plurality of raised ribs on the said wings.
 4. The apparatus according to claim 1 wherein the means for securing the board drain to said capping means comprises a pair of tongues spaced from each other, said tongues being mounted in said capping means, said board drain being mounted between said tongues, and means for securing said board drain to said tongues.
 5. The apparatus according to claim 4 wherein said tongues are provided with a plurality of protuberances and said board drain is provided with a plurality of apertures, said protuberances engaging said apertures when said board drain is in place between said tongues.
 6. The apparatus according to claim 1 wherein said means for securing said board drain to said capping means comprises a tongue mounted on said capping means, said board drain being mounted adjacent one face of said tongue, and fastening means for securing said board drain to said tongue.
 7. The apparatus according to claim 1 wherein said board drain is made of water resistant craft paper.
 8. The apparatus according to claim 1 wherein said board drain is made of sintered porous polyvinyl chloride. 